Mesoscale Mechanisms Research Articles

3D image visualization of meso-structural changes in a bimsoil under uniaxial compression using X-ray computed tomography (CT)

In situ quantification of the meso-structural changes in block-in-matrix-soils (bimsoil) is crucial for stability predictions. While the macroscopic failure of bimsoil has been widely studied, the physical meso-scale mechanisms governing bimsoil deformation have not been well understood. Here, high energy X-ray computed tomography (CT) measurements were performed on a bimsoil sample with a rock block percentage (RBP) of 40% under uniaxial compression to collect three-dimensional data for the sample's meso-damage evolution. The 3D pattern of the sample deformation was imaged in real-time, and meso-structural changes are visualized by the rendered CT images. The data showed that cracks propagated by passing rock blocks, leading to a macroscopic fracture with a well-developed twisting characteristic. The crack rose diagram reveals the propagation path of the cracks, which are mostly parallel to the loading direction. In addition, interlocking occurs during the propagation of cracks, which determined the curved morphology of the fracture plane. Moreover, the fractal 3D digital image analysis quantifies the complexity of the crack distribution with increasing sample deformation. This work demonstrates the strong influence of local mechanical variations due to existing rock blocks on the crack propagation in bimsoil.

A Second Generation Multiphase-CFD Framework Toward Predictive Modeling of DNB

Building on the strong belief that the advancement and consistent adoption of cutting-edge simulation tools is critical to the future of nuclear power, three-dimensional thermal-hydraulic methods in the form of computational fluid dynamics (CFD) have made enormous advancement and promise to transform the way we approach the design of more efficient and reliable systems. The success of these methods hinges on the accuracy and predictive ability of the underlying models, which must, at the same time, limit the computational cost and allow optimal scalability. A large effort at the Massachusetts Institute of Technology has been devoted to the development of a second-generation of multiphase-CFD (M-CFD) closures and to leveraging the continuous progression in the experimental techniques. Among the numerous objectives, the central challenge that has driven the overall approach is the prediction of departure from nucleate boiling. This work focuses on deriving the fundamental meso-scale mechanisms from the CFD-grade experiments and incorporates them in the M-CFD framework as subgrid-scale models. A more complete representation of lateral lift force and near-wall effects are proposed, in combination with direct numerical simulation–driven understanding of bubble-induced turbulence effects. The improved description of the multiphase flow distribution is coupled to a novel representation of boiling heat transfer, which aims at introducing all the physical mechanisms that are encountered at the boiling surface. Starting from the improved representation at the wall, this work concentrates on the micro-hydrodynamics of the thin liquid film on the heated surface, which governs the critical heat flux limit.

Investigation of mesostructural changes in bimsoil during triaxial deformation: an insight using X-ray computed tomography and ultrasonic measurement

In this paper, mesoscopic structural changes and the associated strain localization behaviors were investigated quantitatively using X-ray computerized tomography (CT) and ultrasonic measurement techniques. While the effects of rock blocks on the macroscopic mechanical of block-in-matrix soil (bimsoil) have been widely studied, the physical mesoscale mechanisms governing the bimsoil deformation are still poorly understood. Triaxial compression experiment was conducted on bimsoil sample with rock proportion of 30% (mass ratio). The mesostructural changes were quantitatively studied using macroscopic stress-strain description and mesoscopic CT image identification. Under triaxial compression, the stress-strain curve of bimsoil presents strain hardening behavior, and the interactions between rock block and soil matrix result in the strain localization and mesostructural changes. In addition, the damage evolution behaviors of bimsoil are different from soil and rock, and spatial kinematic of rock blocks results in not only the fluctuation of CT value, ultrasonic pulse velocity (UPV), and transmitted ratio (TR) but also the crack geometry characteristics (e.g., length, area, width, and fractal dimension). What is more, contaction and separation between soil matrix and rock block occur repeatedly during sample deformation, and the fractal dimension of the crack distribution becomes larger. Through a series of mesostructural change analysis, the mesomechanisms of bimsoil under triaxial deformation have been first discussed.

Three-dimensional observations of meso-structural changes in bimsoil using X-ray computed tomography (CT) under triaxial compression

In situ quantification of the meso-structural changes in block-in-matrix-soils (bimsoil) is crucial to the stability prediction of construction and building structures made of bimsoil. While the macroscopic failure of bimsoil has been widely studied, the physical meso-scale mechanisms governing bimsoil deformation have not been well understood. Here, high energy X-ray computed tomography (CT) measurements were performed on a bimsoil sample with rock block percentage (RBP) of 30% under triaxial compression, in order to collect three dimensional data on rock blocks and crack distribution. The 3D meso-structural changes have been visualized in real-time during triaxial deformation. The results showed that cracks propagated by passing rock blocks, leading to a macroscopic fracture with well-developed tortuous. In addition, interlocking occurs during the propagation of cracks, and the 3D pattern of the macroscopic fracture surface has been revealed from the reconstructed CT volume data. Moreover, rock-soil interface slippage, large pore formation, crack interlocking and growth together lead to formation of localization deformation. The localization deformation becomes obvious as axial strain grows, which can be reflected by the increasing 3D fractal dimension of the sample density distribution. This demonstrates the large control of local mechanical variations on the crack propagation in bimsoil, which is caused by existing rock blocks on. Through a series of meso-structural evolution analysis, the meso-mechanisms of localized deformation for bimsoil under triaxial deformation have been first documented.

Local Enhancement of Extreme Precipitation during Atmospheric Rivers as Simulated in a Regional Climate Model

Abstract This paper examines the synoptic conditions that yield extreme precipitation in two regions with different orographic features, the Olympic Mountains and Puget Sound. To capture orographic extreme precipitation, a dynamical downscaling is performed, driven by the NCEP–NCAR reanalysis and evaluated for cool-season months from 1970 to 2010. Clustering techniques are applied to the regional climate simulation, which reveals the Olympic Mountains and Puget Sound as regions with distinct temporal variability in precipitation. Results show that approximately one-third of the extreme precipitation events in each region occur without a similarly extreme event in the other, in spite of the fact that the two areas are very closely located and one is downstream of the other. Composites of synoptic conditions for extreme precipitation events show differences in integrated vapor transport (IVT) due to its dynamical component (winds at 850 hPa) and its thermodynamical component [integrated water vapor (IWV)]. For Puget Sound events, IVT is lower compared to Olympic Mountain events because of lower wind speeds. Olympic Mountain events have lower IVT compared to events with extreme precipitation in both regions, but in this case, the difference is due to lower IWV and more southerly winds. These differences in the large-scale conditions promote differences in the mesoscale mechanisms that enhance precipitation in each location. For Puget Sound events, static stability is higher, and there is a weak rain shadow. For Olympic Mountain events, static stability is lower, and a strong rain shadow is present. During extreme events in both regions, orographic modulation is minimized and large-scale effects dominate.

Mesoscale and submesoscale mechanisms behind asymmetric cooling and phytoplankton blooms induced by hurricanes: a comparison between an open ocean case and a continental shelf sea case

Right-side bias in both sea surface cooling and phytoplankton blooms is often observed in the wake of hurricanes in the Northern Hemisphere. This idealized hurricane modeling study uses a coupled biological-physical model to understand the underlying mechanisms behind hurricane-induced cooling and phytoplankton bloom asymmetry. Both a deep ocean case and a continental shelf sea case are considered and contrasted. Model analyses show that while right-side asymmetric mixing due to inertial oscillations and restratification from strong right-side recirculation cells contributes to bloom asymmetry in the open ocean, the well-mixed condition in the continental shelf sea inhibits formation of recirculation cells, and the convergence of water onto the shelf is a more important process for bloom asymmetry.

Pathway-controlled formation of mesostructured all-DNA colloids and superstructures.

DNA has traditionally been used for programmable design of nanostructures exploiting its sequence-defined supramolecular recognition. However, control on larger lengths scales or even hierarchical materials translating to the macroscale remain difficult to construct. Here, we show that the polymer character of ssDNA can be activated via a nucleobase-specific lower critical solution temperature (LCST), providing unique access to mesoscale structuring mechanisms on larger length scales. We integrate both effects into ssDNA multiblock copolymers coding sequences for phase-separation, hybridization, and functionalization. Kinetic pathway guidance using temperature ramps balances the counteracting mesoscale phase-separation during heating with nanoscale duplex recognition during cooling, yielding a diversity of complex all-DNA colloids with control over internal dynamics and of their superstructures. Our approach provides a facile and versatile platform to add mesostructural layers into hierarchical all-DNA materials. The high density of addressable ssDNA blocks opens routes for applications like gene delivery, artificial evolution, or spatially encoded (bio)materials.

Multi-scale finite element analysis for tension and ballistic penetration damage characterizations of 2D triaxially braided composite

The multi-scale finite element model is presented to analyze tension and ballistic penetration damage characterizations of 2D triaxially braided composite (2DTBC). At the mesoscopic level, the damage of fiber tows is initiated with 3D Hashin criteria, and the damage initiation of pure matrix is predicted by the modified von Mises. The progressive degradation scheme and energy dissipation method are adopted to capture softening behaviors of tow and matrix. The macro-scale damage model is established by maximum-stress criteria and exponential damage evolution. To simulate interface debonding and inter-ply delamination, a triangle traction–separation law is adopted in each scale. Both scale damage models are verified with available experimental results. Based on numerical predictions, the stress–strain responses and damage developments of 2DTBC under axial and transverse tension loading are studied. For ballistic penetration loading, the meso-scale damage mechanisms of 2DTBC are predicted using 1/4 model, 1/2 model, 1-layer model, 2-layer model and 3-layer model. Then, effects of different model and impactor radius on damage modes are analyzed. Additionally, the macro-scale ballistic penetration behaviors of 2DTBC are simulated and compared with experiment. The prediction results for tension and penetration correlate well with experiment results. Both tension and penetration damage characterizations for tow, matrix within tow, pure matrix, interface and inter-ply delamination are revealed. A comparison of penetration damage between meso- and macro-scale presents a similar crack mechanism between two scales.

Mesoscale and Submesoscale Processes in the Southeast Atlantic and Their Impact on the Regional Thermohaline Structure

AbstractThe turbulent processes in the Cape Basin, the southeasternmost gate of the Atlantic Ocean, play a key role in the transport and mixing of upper to intermediate water masses entering the area from the Indian Ocean, making them especially relevant for the Indo‐Atlantic transfer of heat and salt. In this paper, two numerical simulations at different horizontal resolutions are used to study mesoscale and submesoscale dynamics, their phenomenology, their evolution, and their impact on the local water masses. Submesoscale processes seasonally affect both, the upper and intermediate layers, but there are clear dynamical differences between the two layers. Several types of instabilities underline this spatial and temporal variability. Near the surface, mixed layer instabilities occur during winter, while mesoscale‐driven instabilities, as the symmetric type, prevail in summer. The connection between these two seasonal regimes is ensured, in anticyclonic eddies and within the mixed layers, by Charney baroclinic instabilities, involved in the local formation and subduction of mode water, that we have dubbed as Agulhas Rings mode water. Intermediate depths are instead characterized by mesoscale mechanisms of density compensation and lateral stirring of the tracer variance, triggering a significant filamentogenesis whose vertical scales are comparable to those mentioned in previous studies. This leads to a particularly efficient mixing of Antarctic Intermediate Waters of Indian and Atlantic origins. Lagrangian estimates highlight the new and significant role of fine scale structures in setting the water masses properties of upper and lower thermocline waters materializing the Indo‐Atlantic exchange and therefore potentially affecting the global ocean circulation.

Topological dynamics of vortex-line networks in hexagonal manganites

Hexagonal manganites REMnO3 (RE, rare earths) have attracted significant attention due to their potential applications as multiferroic materials and the intriguing physics associated with the topological defects. The two-dimensional (2D) and 3D domain and vortex structure evolution of REMnO3 is predicted using the phase-field method based on a thermodynamic potential constructed from first-principles calculations. In 3D spaces, vortex lines show three types of topological changes, i.e. shrinking, coalescence, and splitting, with the latter two caused by the interaction and exchange of vortex loops. Compared to the coarsening rate of the isotropic XY model, the six-fold degeneracy gives rise to negligible differences with the vortex-antivortex annihilation controlling the scaling dynamics, whereas the anisotropy of interfacial energy results in a deviation. The temporal evolution of domain and vortex structures serves as a platform to fully explore the mesoscale mechanisms for the 0-D and 1-D topological defects.

Use of X-ray computed tomography to investigate the effect of rock blocks on meso-structural changes in soil-rock mixture under triaxial deformation

Construction and building of engineering structures in geomaterials with soil and rock mixture (SRM) are often challenging tasks for engineers. While the effects of rock block content on the macroscopic mechanical properties have been widely studied, the physical meso-scale mechanisms governing the SRM deformation are still poorly understood. Here, we applied a high energy X-ray Computed Tomography (CT) imaging method to study the influence of rock block content on the mesoscopic structural changes and the associated strain localization behaviors in SRM. Triaxial compression experiment was conducted for the SRM samples with rock block percentage (RBP) of 0%, 30%, 40%, and 50%, respectively, under a confining pressure of 120 kPa. The meso-structural changes were quantitatively studied using the macroscopic stress–strain descriptions and mesoscopic CT images identification. Under triaxial deformation, the stress–strain curves present strain hardening behavior, strength of the sample increases with increasing RBP, which can be verified from the interlocking of rock blocks, and skeleton role of blocks improves the capacity to resist deformation. In addition, regions of localization are extremely non-uniform and strongly affected by the rock blocks, scale of the localized bands presents a incremental trend as RBP increases. What is more, the most striking observation from the reconstructed images is that zone of localization may disappear during deformation owing to the interactions between the rock block and soil matrix. Through a series of meso-structural evolution analysis, the meso-mechanisms of the effect of rock block content on SRM under triaxial deformation have been documented.

Mesoscale ballistic damage mechanisms of a single-layer woven glass/epoxy composite

Understanding damage mechanics across multiple length scales is necessary for design of enhanced protection by composite armor systems. In this work, we investigated the perforation mechanics of a single layer, woven composite target transversely impacted below and above the ballistic limit by a rigid projectile sized on the order of a tow width. To visualize mesoscale damage mechanisms of woven composites, a thin translucent composite target was used providing access to both impact and back-face surfaces. High-speed video, high-speed digital image correlation, high-resolution photography, and X-ray computed tomography were used to gather data. Impact and residual velocity data, ballistic limit velocity, and projectile impact location relative to the weaving architecture were quantified. It was found that impact on a tow-tow crossover requires more energy to perforate than impact on a matrix-rich interstitial site or on adjacent, parallel tows. Dynamic deflection and the transverse deformation cone wave-front velocity of the thin composite were measured. Meso-mechanical damage in thin, woven composites was characterized for impact velocities below and above the ballistic limit. Four mesoscale damage modes were identified: transverse tow cracks, tow-tow delamination, 45° matrix cracks, and punch-shear. These damage modes were observed both on the surface and inside the composites. The data presented here are useful for mesoscale modeling of woven composites, and this work provides new insight into meso‑mechanical modes of damage in thin composite structures under dynamic impact.

Meso-scale mechanism of compaction shock propagation in cellular materials

The meso-scale mechanism of a compaction shock in a cellular material is investigated numerically using a 2D Voronoi cellular model. The compaction shock is initiated by the compression of a 2D Voronoi cellular model at constant velocities sufficiently higher than the critical shock velocity. The compaction shock is featured by the propagation of a nearly planar (1D) shock front, across which, macroscopic physical quantities (i.e. stress, strain, particle velocity and density) show strong discontinuity. The 1D cross-sectional stress in the Voronoi model is decomposed into deformation-induced stress and contact-induced stress. It shows that the contact-induced stress plays a dominant role in the shock stress enhancement in dynamic compression. It is shown that the velocity-dependent inertia term in the 1D shock stress equation derived from conservation laws in continuum mechanics is the contact-induced stress produced by the internal collisions of cell walls in meso-scale at the compaction shock front. The internal collisions accelerate the adjacent layer of cell walls to the compression velocity rapidly, and a velocity discontinuity at the shock front is formed for the next internal collision. Meanwhile, the local cell-wall acceleration leads to an inertial pulse of the deformation-induced stress, which is generally smaller than the contact-induced stress. It is found that the stress distribution in the region ahead of shock-front is non-uniform. These findings reveal the meso-scale mechanisms of the compaction shock propagation in cellular materials subjected to intensive dynamic loads.

A coarse-grained model for the mechanical behavior of graphene oxide

Graphene oxide (GO) shows promise as a nanocomposite building block due to its exceptional mechanical properties. While atomistic simulations have become central to investigating its mechanical properties, the method remains prohibitively expensive for large deformations and mesoscale failure mechanisms. To overcome this, we establish a coarse-grained (CG) model that captures key mechanical and interfacial properties, and the non-homogeneous effect of oxidation in GO sheets. The CG model consists of three types of CG beads, representing groups of pristine sp2 carbon atoms, and hydroxyl and epoxide functionalized regions. The CG force field is parameterized based on density functional-based tight binding simulations on three extreme cases. It accurately quantifies deterioration of tensile modulus and strength at the expense of improving interlayer adhesion with increasing oxidation of varying chemical compositions. We demonstrate the applicability of the model to study mesoscale phenomena by reproducing different force vs. indentation curves in silico, corroborating recent experimental observations on how chemistry near contact point influences properties. Finally, we apply the model to measure the fracture toughness of pristine graphene and GO. The critical stress intensity factor (Kc) of graphene is found to be the highest, and epoxide-rich GO also possesses higher Kc compared to hydroxyl-rich GO.

Meso-scale fracture simulation using an augmented Lagrangian approach

A cohesive zone model implemented in an augmented Lagrangian functional is used for simulation of meso-scale fracture problems in this paper. The method originally developed by Lorentz is first presented in a rigorous variational framework. The equivalence between the stationary point of the one-field problem and the saddle point of the mixed formulation is proved by solving the double inequality of the mixed functional. An adaptation to simulate fracture phenomena in the meso-scale via mesh modification is also presented as an algorithm to insert zero-thickness interface elements based on Lagrange multipliers, boarding the non-trivial task of the field interpolation for different crack paths (plain and tortuous). A suitable tool to study the matrix fracture and debonding phenomena in composites with strongly different component stiffnesses that avoids ill-conditioning matrices associated with intrinsic cohesive zone models is obtained. The method stability is discussed using a simple patch test. Some numerical applications to fracture problems taking into account the mesostructure and, particularly, the study of transverse failure of longitudinal fiber reinforced epoxy and the fracture in concrete specimens are included in the paper. Comparing the numerical results with the experimental results obtained by other researchers, the paper introduces a discussion about the influence of coarse aggregate volume in meso-scale fracture mechanisms in concrete L-shaped specimens.

Differences in the Climatological Characteristics of Precipitation between Active and Break Spells of the Indian Summer Monsoon

Abstract Climatological characteristics of precipitation during the active and break spells of the monsoon are studied using 15 years of TRMM measurements. The spatial variation of rain fraction suggests that most of the seasonal rainfall occurs in spells of active monsoon over India, except for the zones along the east coast. The broader reflectivity distribution at higher altitudes and larger average storm height during active spells indicate the high prevalence of deep systems during this spell. The spatial distribution of the occurrence and fraction of different types of rain exhibits large variability from land to ocean and between the spells. The higher occurrence and fraction of stratiform rain during the active spell, particularly over the core monsoon zone, is due to the prevalence of organized mesoscale systems with large stratiform portions. The break spells are characterized by higher occurrence of shallow rain and larger fraction of convective rain. While an evening peak is observed over land during the break spell, the phase of the diurnal cycle exhibits large spatial variability during the active spell. The rainfall peaks from late night to midnight in southeastern India and in the morning near the foothills of the Himalayas during the active spell. The diurnal and semidiurnal components together explain more than 90% of total variance over many of the zones during both spells. The observed differences in precipitation between the spells are discussed in light of the differences in synoptic- and mesoscale mechanisms responsible for the production of precipitation.

Seasonal and spatial variability of surface chlorophyll inside mesoscale eddies in the South China Sea

Mesoscale eddies can influence biogeochemical cycles through both vertical nutrient or plankton flux and horizontal advection of nutrient or plankton in eddy periphery. In this study, we analyzed the seasonal and spatial variability of near-sea-surface chlorophyll-a concentrations and their corresponding modulation mechanisms by collocating satellite observations of eddies tracked during 1998–2007 in the South China Sea. We found that in winter, cyclonic eddies show significantly high chlorophyll-a in the eddy core relative to the periphery, suggesting regulation by an eddy-pumping mechanism. While in summer, chlorophyll-a values in the core of cyclonic eddies are comparable with those in the periphery, and dipole features of chlorophyll-a around cyclonic eddies are conspicuous, which is largely induced by horizontal eddy advection. For anticyclonic eddies, however, low chlorophyll-a in eddy cores compared with the periphery are consistently present over most of the year. The impact of eddy advection on chlorophyll-a distribution in anticyclonic eddies is not clear from the composite images in different seasons. Variability of chlorophyll-a to the west of the Luzon Strait and northwest of the Luzon Island demonstrate that phytoplankton biomass in these two regions is mainly controlled by an eddy-pumping mechanism. In the regions off the Vietnam coast, chlorophyll-a distributions are generally associated with horizontal eddy advection. This research highlights different mesoscale mechanisms affecting biological structures in the upper ocean, which can potentially disturb ocean biogeochemical cycling processes in the South China Sea.

Using simulations with realistic fibrous network geometry to determine the achievable ranges of macroscopic mechanical behaviors of elastomeric scaffolds

Event Abstract Back to Event Using simulations with realistic fibrous network geometry to determine the achievable ranges of macroscopic mechanical behaviors of elastomeric scaffolds Michael S Sacks1, 2 and Greg Rodin2 1 The University of Texas at Austin, Biomedical Engineering, United States 2 the University of Texas at Austin, Department of Aerospace and Mechanical Engineering, United States Introduction: Tissue engineers seek to produce tissues that function biologically and mechanically as well as the native tissues they are built to replace. This macroscopic behavior is strongly influenced by the evolution of the complex microstructural geometry of the underlying scaffold. Elastomeric scaffolds manufactured by the electrospinning process produces layers of long-fiber networks. It has been found that knowledge of the fiber properties, fiber density, and orientation density function are sufficient to predict the bulk mechanical behavior. However, the micro- and meso-scale mechanisms responsible for the behavior remain unclear. Initial simulations based on experimentally derived geometry suggest that the load induced emergence of long fiber paths may be a mechanism contributing to the observed bulk mechanical behavior. Methods: The purpose of this study was to develop and utilize computational models, based on realistic fiber geometry, to understand the mechanisms that translate scaffold fiber network structure into tissue simulating function. We also explored the range of macroscopic material behaviors that are achievable from the domain of producible microstructural geometries and elastomeric fiber properties, both essential first steps in developing the ability to design engineered tissues that mimic native tissue behavior. Results: We performed 3-D, non-linear micromechanical simulations of layers of long-fiber networks, generated using a random walk procedure that mimics the scaffold structure. Using these realistic fiber networks, we are able to investigate the mechanisms responsible for the stress-strain curve in ways not possible previously. For example, by independently varying the initial geometric anisotropy and the initial tortuosity, we separated the effects of each of these variables on the nonlinearity of the stress-straincurve. Discussion: Insights such as these inform macroscale material models that can be used to guide the design of scaffolds and the selection of manufacturing parameters so that the resulting engineered tissues mimic the non-linear mechanical behavior of the native tissues. NIH R01 HL68816 Keywords: modeling, Scaffold, microstructure, 3D scaffold Conference: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016. Presentation Type: Poster Topic: Computational modeling in biomaterials science and engineering Citation: Sacks M and Rodin G (2016). Using simulations with realistic fibrous network geometry to determine the achievable ranges of macroscopic mechanical behaviors of elastomeric scaffolds. Front. Bioeng. Biotechnol. Conference Abstract: 10th World Biomaterials Congress. doi: 10.3389/conf.FBIOE.2016.01.03023 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 28 Mar 2016; Published Online: 30 Mar 2016. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Michael S Sacks Greg Rodin Google Michael S Sacks Greg Rodin Google Scholar Michael S Sacks Greg Rodin PubMed Michael S Sacks Greg Rodin Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The relation between circulation types and regional Alpine climate. Part I: synoptic climatology of Trentino

ABSTRACTA comprehensive data set of surface temperature, rainfall, solar radiation and wind measurements was composed to investigate the relation between synoptic circulation types and the climate of Trentino, a mountainous region in the South‐Eastern Alps. Synoptic patterns are classified over different levels by means of an existing classification method according to their degree of zonality, meridionality and vorticity. Distinct seasonal anomalies of mean daily temperature, total daily rainfall, daily solar irradiation and mean daily wind intensity are associated with most circulation types. Their magnitude varies not only among weather types, but also within the same type for different isobaric levels and seasons. The largest positive temperature anomalies are observed in correspondence with high‐pressure and westerly circulations, whereas southerly circulation in the upper levels and low‐pressure systems at lower altitudes produce the largest positive deviations of daily rainfall. Daily solar irradiation and mean daily wind intensity are larger than average with northerly circulations. Particular emphasis is given to extreme meteorological events, which occur with preferential circulation types. In fact, the frequency of occurrence of extremes of any variable for each synoptic pattern rarely coincides with the climatological value. Even though extremes in daily rainfall are observed with almost all synoptic circulations, most of them occur with the south‐westerly circulation at 500 hPa, a frequent configuration contributing more than 50% to the total rainfall. Moreover, they occur with a larger variety of weather types at the lower levels and in spring and summer with respect to the upper levels and the colder seasons. The large number of statistical indices presented in this paper reveals that the climate of Trentino is strongly influenced not only by the synoptic circulation, but also by the mesoscale mechanisms resulting from the interaction of the large‐scale flow with the local orography.

The mechanisms of plastic strain accommodation during the high strain rate collapse of corrugated Ni–Al laminate cylinders

The Thick-Walled Cylinder method was used on corrugated Ni–Al reactive laminates to examine how their mesostructures accommodate large strain, high strain rate plastic deformation and to examine the potential for intermetallic reaction initiation due to mechanical stimuli. Three main mesoscale mechanisms of large plastic strain accommodation were observed in addition to the bulk distributed uniform plastic flow: (a) the extrusion of wedge-shaped regions into the interior of the cylinder along planes of easy slip provided by angled layers, (b) the development of trans-layer shear bands in the layers with orientation close to radial and (c) the cooperative buckling of neighbouring layers perpendicular to the radius. These mesoscale mechanisms acted to block the development of periodic patterns of multiple, uniformly distributed, shear bands that have been observed in all previously examined solid homogeneous materials and granular materials. The high-strain plastic flow within the shear bands resulted in the dramatic elongation and fragmentation of Ni and Al layers. The quenched reaction between Al and Ni was observed inside these trans-layer shear bands and in a number of the interfacial extruded wedge-shaped regions. The reaction initiated in these spots did not ignite the bulk of the material, demonstrating that these mesostructured Ni-Al laminates are able to withstand high-strain, high-strain rate deformation without reaction. Numerical simulations of the explosively collapsed samples were performed using the digitized geometry of corrugated laminates and predictions of the final, deformed mesostructures agree with the observed deformation patterns.